The present invention concerns a reinforced laminated structure for composite material, which structure comprises a stack of superimposed layers of bi-dimensional reinforcing material and rectilinear reinforcing elements traversing said stack through and through.
The field of application of the invention is that of tridimensional reinforcement structures used in the manufacture of composite materials. These are obtained by filling the structures with a matrix. Such composite materials are intended to be used in particular in the production of parts meant to be subjected to special conditions such as strong mechanical or thermal stresses.
Laminated reinforcement structures are constituted by superimposed layers of bi-dimensional type reinforcing material such as fabrics, unidirectional sheets, felts, papers, etc. . . . The laminated composite materials formed with such structures have a defect in common, that is breakage through delamination due to the weakness of the bondings between the layers of materials.
In order to overcome this disadvantage, it was proposed to reinforce laminated structures by adding reinforcing elements thereto in a direction perpendicular to the plane of the layers, which elements traverse the stack through and through. A tridimensional-type reinforced laminated structure is thus obtained. The reinforcing elements are either wires, or small rigid rods which can also comprise a fibrous reinforcement. The whole assembly of reinforcement elements forms a bundle of virtually rectilinear reinforcing elements, which are parallel together and distributed either in regular manner or at random with respect to the surface of layers.
In practice, it was noted that such an arrangement of transverse reinforcement elements only brings but a small protection against delamination because of the possibility for part of the stacked layers to slide along the bundle of reinforcing elements and to come apart from the rest of the stack. Although this coming apart does not necessarily lead to a complete breakage as with the delamination of a non-reinforced laminated structure, it is nevertheless a serious disadvantage which shows that this particular solution is not perfect yet.
It is the aim of the invention to propose a reinforced laminated structure permitting to remove any subsequent possibility of decohesion of the stacked layers of the composite material.
This aim is reached because, according to the invention, the reinforcement elements are arranged in at least two different directions, each reinforcing element being at an angle with the plane that is tangential to the layers it traverses, and at least one of said directions being at an angle with the perpendicular to the traversed layers.
According to that arrangement of the reinforcing elements, the reinforcing elements found in every part of the stack, are oriented differently with respect to one another, thereby constituting a locking for the contacting layers.
This result may be obtained by an arrangement at random of the reinforcing elements both in their distribution with respect to the surface of the layers and in their orientation with respect to the planes tangential to the layers.